The thing is, how many improvements did we need to mention and justify for 4 marks? I personally answered it like a 6 marker and went into detail heaps but I don't know what would have been necesary to get all 4 marks by writing the bare minimum.There were some more obvious issues with the method. They used 200mL acid rather than like 50mL acid to 150mL water, the acid was dilute when it should have been concentrated, they filtered the dissolved before adding Barium Chloride which was wrong, they added the Barium Chloride quickly when they should have added slowly, etc.